I've just spent my first wipe night on this boss, I can sympathise to an extent with the OP, on 25 man I am tanking 2 dogs and having to manage all of the taunts (and shout at the odd melee who seems to think they can stand and dps whilst chained to the Tile person) whilst staying on top of my active mitigation can be pretty horrible. I played what I would consider to be pretty horribly and come out with 64% shuffle and 75% EB, this will go up alot when I am not playing like a tard and don't have to babysit people with chains etc. Shuffle time and EB time is really key and getting 400k Guards is also nice
I've been running with soft caps and all out haste, which I don't feel a horrible amount of difference from hard capping.
As for the playing an "easy" tank class previously, I tanked all of DS heroic on 25 man as a warrior (dps mainspec) and I don't see that as a stumbling block, but I think my dps mentality has helped ease the transition, as alot of dps classes have to micro manage several buffs and pre plan their burst (or in this case active mitigation). I like it alot as it's much more involved, I used to fall asleep tanking on my warrior after the threat buff.